[PATCH] libstdc++:Fixed the bug in std::system_category.message(int) on Windows

[Jonathan Wakely]

On Sun, 21 Dec 2025, 19:44 Wang Jinghao, <zheng.xianyuwang@gmail.com> wrote:

> Ignoring FORMAT_MESSAGE_IGNORE_INSERTS when retrieving system
> error messages from FormatMessage may result in unexpected error messages
> and
> trigger new exceptions.


For those like me who have no idea what this is about, this explains it:
https://devblogs.microsoft.com/oldnewthing/20071128-00/?p=24353

Can we add a test with error code 87?


This patch changes the
> std::system_category.message(int) to be the same as the flags in
> gcc/plugin.cc:win32_error_msg()
>
> libstdc++-v3/ChangeLog:
>
>         * src/c++11/system_error.cc:
>

This changelog entry is missing a description.


---
>  libstdc++-v3/src/c++11/system_error.cc | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/libstdc++-v3/src/c++11/system_error.cc
> b/libstdc++-v3/src/c++11/system_error.cc
> index b9a0b2c158f..ea7b5cd1226 100644
> --- a/libstdc++-v3/src/c++11/system_error.cc
> +++ b/libstdc++-v3/src/c++11/system_error.cc
> @@ -162,7 +162,9 @@ namespace
>        char* buf = nullptr;
>        auto len
>         = FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM
> -                       | FORMAT_MESSAGE_ALLOCATE_BUFFER,
> +                       | FORMAT_MESSAGE_ALLOCATE_BUFFER
> +                       | FORMAT_MESSAGE_IGNORE_INSERTS
> +                       | FORMAT_MESSAGE_MAX_WIDTH_MASK,
>                         nullptr,
>                         i,
>                         LANG_USER_DEFAULT,
> --
> 2.52.0
>
>
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